how does WI affect spool?

[hotrod]

Yes and Yes (sorta).

Yes spraying too early will slow down the spool up. That is why most folks do not trigger the WI until they get up near 70% or so of max boost.

As far as helping a turbo with a small hotside, it will probably help some but not a lot. If you cool the exhaust gas too much, although the gas volume drops, so does the speed of sound in the exhaust flow, and that changes the maximum speed that gasses can pass through the throat of the turbine. Cooler gasses reach sonic flow at lower speeds so you won't gain as much as you might hope.

Larry